1. Field of the Invention
The present invention relates to a crystallization method and a crystallization apparatus for generating a crystal products having a narrow particle size distribution width and a predetermined particle size.
2. Description of Related Art
Conventionally, batch cooling crystallization has been performed, in which the temperature of a solution obtained by dissolving a compound (substance to be extracted as crystals) is dropped to thereby precipitate the compound and generate crystals, using as a driving force, a difference between a supersaturated state of the solution caused due to the temperature drop, and the concentration of the saturated compound.
Crystallization means that a particular compound is separated from a liquid phase by precipitating the crystals from the liquid phase.
In cooling crystallization, a cooling temperature profile at the time of cooling a solution is perceived to be important, and as cooling methods having different cooling temperature profiles, a controlled cooling method, a linear cooling method, and a natural cooling method have been devised (for example, refer to Non-Patent Document 1). Among these cooling methods, according to the controlled cooling method, a supersaturation of a saturated solution is maintained low and constant from beginning to end by decreasing the temperature change (slowing down the cooling speed) in an initial stage when an amount of crystals is small, and increasing the temperature change (accelerating the cooling speed) at the time of termination when the amount of crystals increases. Accordingly, secondary nucleation is suppressed, and only monodispersed particles are obtained.
As a general batch cooling crystallizer for performing crystallization process, one having a crystallization tank with an agitator is used. As such a crystallizer, for example, there is disclosed an apparatus that supplies a solution including a seed crystal and a compound into a crystallization tank, and causes an agitator provided in the crystallization tank to perform paddling motion in the figure eight, to thereby generate a slow and large swirling current of the solution in the crystallization tank (for example, refer to Patent Document 1).    [Patent Document 1] Japanese Unexamined Patent Application, First Publication No. 2007-313484    [Non-Patent Document 1] “Industrial Crystallization Operations—New Edition”, page 5, issued on Jan. 31, 2006, Editor: The Society of Separation Process Engineers, Japan, Publication office: The Society of Separation Process Engineers, Japan
Incidentally, the above-described controlled cooling method is considered to be effective in cooling crystallization using a seed crystal (seeding). However, even if the controlled cooling method is executed, there is not much difference with regard to particle size distribution by weight of a product after finishing crystallization, as compared with a case where a cooling method having other cooling temperature profiles (linear cooling method, natural cooling method) is executed, and the monodispersed particles can not be obtained stably after finishing crystallization.
Moreover, in the crystallizer disclosed in Patent Document 1, because generated crystal particles collide with each other repeatedly due to agitation of the solution in the crystallization tank by the agitator, the crystal particles are disrupted, and the particle size may become different.
In one embodiment, a crystallization method and a crystallization apparatus that can generate monodispersed particles having a narrow particle size distribution width in the cooling crystallization without seed crystals is described. Moreover, a crystallization method and a crystallization apparatus that can generate monodispersed particles having a narrow particle size distribution width, even if nucleation timing of crystal particles is different for each batch are disclosed.